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Original question:

AM5728: PMIC(TPS6590377ZWSR) POWER GOOD signal pull low

TPS659037: Reset of AM5728 when Linux is starting

Robert Pot
Prodigy 150 points
Part Number: TPS659037
Other Parts Discussed in Thread: AM5728,

Hi,

my question is related to the issue mentioned in https://e2e.ti.com/support/power-management/f/196/p/738631/2727879

We see the exact same situation as that the PMIC is resetting the AM5728 CPU although this is not only happening at -40 degrees but some boards have this issue already at room temperature.
In that case the board is resetting about 10 times(with intervals of maybe 2 seconds) and when the system is warmed up a little it doesn't happen anymore and works properly.
Not all boards have this issue but most do.

It is our own board using SDK 05.00.00.15 as basis

When the board starts u-boot it starts normally and when I interrupt the startup sequence of u-boot the board is working fine. But when Linux is starting the CPU is reset. I guess this is due to the fact that the power consumption is increasing. We see the same behavior on the scope screens as shown in the related issue.

At the moment my first question is if there was a solution found to the above mentioned article. It stopped without a solution and also I couldn't find any other message with the same issue.

Regards, Robert

  • 0
    TI__Genius 10000 points

    Robert,

    The thread you are referring to did not have enough information to come to a resolution.

    The TPS659037 will reset if any of the "OFF Requests" (table located in the datasheet) are executed. POWERGOOD was discussed in the other thread, but this pin is only a monitoring pin, and does not reset the processor unless your system is set up to do so. Are you saying that POWERGOOD is connected to the PORz of the processor?

    Is there a chance that the software initiates a reset under certain conditions? If so, what conditions are being checked?

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Prodigy 150 points

    Hi Nastasha,

    Yes, indeed the powergood of the PMIC is connected to the PORZ of the CPU. Not directly but the result is the same.

    Is this not wise to do so?

    By default the powergood output is only triggered by the SMPS12 regulator and as far as I know this is not modified by the bootloader. For Linux I don't know.
    Below the schematics of SMP12.
    One error was inductor L1408. We shortened this and this indeed improved the reliability a little bit but still it is not without problems.

    What are the reasons when the SMP12 regulator says it is not good? input voltage, output voltage, output current?

  • 0 in reply to Robert Pot
    TI__Genius 10000 points

    Robert,

    Please pull the latest datasheet off ti.com. We recommend connecting the RESET_OUT pin of the TPS659037 devices to the PORz of the processor, not the POWERGOOD pin. The RESET_OUT pin indicates the PMIC is in ACTIVE mode after the device starts up and remains high until an OFF request is given. Once an OFF request is given from the PMIC, the RESET_OUT pin pulls the PORz pin low and then executes the power down sequence.

    POWERGOOD is only monitoring SMPS12 by default. It is not a recommended way to determine whether the processor should be active for a few reasons:

    1. Since it only monitors SMPS12, it will go high before the whole power sequence is complete. This is not ideal for the processor.

    2. POWERGOOD does not have an internal debounce circuit, where as RESET_OUT does. This means that during fast transient behavior, for multiphase rails (such as SMPS12) the POWERGOOD rail may toggle when there is a brief current spike. Since processors have lots of repetitive transient loading, this is likely why you are seeing the processor turn off/on.

    3. POWERGOOD does not control any sequencing. By using PORz to turn the processor on/off, the processor is not going through its startup and shutdown sequence each time POWERGOOD toggles.

    I would recommend using RESET_OUT as the PORz control and using POWERGOOD as a monitoring-only signal that gets sampled (which adds a deglitch) by the processor before reacting to the signal. See the POWERGOOD section of the datasheet for details on its transient behavior.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Prodigy 150 points

    Nastasha,

    thanks for your answer, we will change this according your suggestions.

    Robert